Dual dc-dc converter

ABSTRACT

A dual DC-DC converter includes a controller signaling a plurality of switch sets for charging a first battery connected to a first DC output and a second battery connected to a second DC output. Each of the switch sets includes a high-side switch configured to switch a DC electrical input to a common node and a low-side switch configured to switch a ground to the common node. A filter capacitor is connected between each of the DC outputs and a ground. A mode switch is connected between the DC outputs and is opened to allow the dual DC-DC converter to be operated with each of the DC outputs having different voltages for independently charging the batteries at different states of charge. The mode switch is closed when the voltages on each of the DC outputs are equal or within a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This PCT International Patent Application claims the benefit of andpriority to U.S. Provisional Patent Application Ser. No. 62/728,300filed on Sep. 7, 2018, titled “Dual DC-DC Converter,” the entiredisclosure of which is hereby incorporated by reference.

FIELD

The present disclosure relates generally to DC-DC converters, and morespecifically to DC-DC converters for battery charging.

BACKGROUND

In some applications, such as in some Electric Vehicles (EVs), it isadvantageous to have two or more low voltage (LV) batteries. Thosebatteries can be used to supply two or more low voltage circuits. It isadvantageous to charge those batteries from a single charger, such as aDC-DC converter, by connecting them together. For example, the batteriesmay be connected in a series or parallel configuration, or in a morecomplex combination thereof. If the charge level of the batteries arenot equal, very high balancing currents will flow from the highercharged battery to the more depleted one when the batteries areconnected. These high currents can reduce the usable lifetime and/or cancause damage to the batteries.

A low voltage balancer (LVB) may be used to balance electrical currentsbetween two or more batteries and to prevent the problem with very highbalancing currents. Such LVB devices are commonly used in recreationalvehicles. However, LVB devices are generally expensive and addadditional cost, complexity, and weight to a vehicle.

SUMMARY

A dual DC-DC converter includes a first switch set having a firsthigh-side switch. The first switch set is configured to generate a firstDC output voltage upon a first output node by selectively closing thefirst high-side switch to couple an input node having a DC input voltageto a first common node. The dual DC-DC converter also includes a secondswitch set having a second high-side switch. The second switch set isconfigured to generate a second DC output voltage upon a second outputnode by selectively closing the second high-side switch to couple theinput node to a second common node. The dual DC-DC converter alsoincludes a mode switch that is configured to selectively couple thefirst output node to the second output node.

A battery charger includes a first switch set configured to control afirst DC output voltage on a first output node and to control a rate ofcharge into a first battery connected thereto. The battery charger alsocomprises a second switch set configured to control a second DC outputvoltage on a second output node and to control a rate of charge into asecond battery connected thereto. The battery charger also includes amode switch that is electrically connected between the output nodes andwhich is operable in a non-conductive mode to provide electricalisolation between the output nodes for allowing the batteries to becharged independently. The mode switch is also operable in a conductivemode to provide electrical continuity between the output nodes.

A method of operating a dual DC-DC converter is also provided. Themethod includes: generating a first DC output voltage upon a firstoutput node by switching a DC input voltage; generating a second DCoutput voltage upon a second output node by switching the DC inputvoltage; and coupling the first output node to the second output nodewith a mode control switch to cause the second output voltage to beequal to the first output voltage with the mode control switch in aclosed condition.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, features and advantages of designs of the inventionresult from the following description of embodiment examples inreference to the associated drawings.

FIG. 1 is a schematic diagram of a DC-DC converter of the prior art;

FIG. 2 is a schematic diagram of a dual DC-DC converter in of thepresent disclosure; and

FIG. 3 is a schematic diagram of another dual DC-DC converter of thepresent disclosure; and

FIG. 4 is a flow chart showing steps in a method of operating a dualDC-DC converter.

DETAILED DESCRIPTION

Recurring features are marked with identical reference numerals in thefigures, in which example embodiments of a dual DC-DC converter aredisclosed.

FIG. 1 illustrates an example of a conventional DC-DC converter 20 forcharging a plurality of batteries 22, 23. The DC-DC converter 20 takeselectrical current on an input node 24 having a DC input voltage V_(IN),which may be, for example, a high voltage such as 400 to 600 VDC andgenerates a DC output voltage V_(OUT) on an output node 26. Thebatteries 22, 23 are shown connected to the output node 26 in a parallelconfiguration. However, the batteries 22, 23 may also be connected tothe output node 26 in series or in a more complex configuration, such asa hybrid series/parallel circuit. A low voltage balancer (LVB) 43 isconnected between the output node 26 and the second battery 23 forregulating current being supplied to or from the second battery 23,which may occur, for example, where the batteries 22, 23 are unbalancedwith different states of charge. The output node 26 may be energized toa predetermined voltage for charging one or more batteries. The DCoutput voltage V_(OUT) may be a low voltage such as, for example, 3 to14 VDC. The DC output voltage V_(OUT) may depend on the particular typeand configuration of the batteries 22, 23 connected to the output node26.

The DC-DC converter 20 includes a controller 30 signaling a plurality ofswitches 32, 34 arranged in switch sets 36, 38 to control the DC outputvoltage V_(OUT) on the output node 26 to its predetermined voltage. Afirst switch set 36 includes a high-side switch 32 configured to switchthe input node 24 to a first common node 40 and a low-side switch 34configured to switch the first common node 40 to a ground 42. A secondswitch set 38 includes a high-side switch 32 configured to switch theinput node 24 to a second common node 41 and a low-side switch 34configured to switch the second common node 41 to the ground 42. Thesecond switch set 38 may be similar in construction and in operation tothe first switch set 36. An inductor 44 is connected between each of thecommon nodes 40, 41 and the output node 26 to limit the current slewrate through the switches 32, 34. In other words, the inductors 44prevent a large voltage spike that may otherwise be induced when theswitches 32, 34 are switched between conducting and non-conducting modesand vice versa. A filter capacitor 46 is connected between the outputnode 26 and the ground 42 to reduce ripple on in the DC output voltageV_(OUT).

The controller 30 may employ known methods, such as pulse widthmodulation (PWM) to control the switches 32, 34. The switches 32, 34 maybe metal oxide semiconductor field effect transistor (MOSFET) typedevices, such as those indicated on FIGS. 1-2, although other types ofdevices may be used such as, for example, other types of field effecttransistors (FETs), triacs, or junction transistors. In someembodiments, one or more of the switches 32, 34 may be insulated gatebipolar transistors (IGBTs) or Gallium Nitride (GaN) transistors.

FIG. 2 illustrates a dual DC-DC converter 20′ according to aspects ofthe present disclosure. Specifically, FIG. 2 illustrates the dual DC-DCconverter 20′ configured as a battery charger for charging a pluralityof batteries 22, 23. However, it should be appreciated that the dualDC-DC converter 20′ may have different applications and/orconfigurations. For example, the dual DC-DC converter 20′ may beconfigured to supply DC power to one or more different loads in additionto or instead of battery charging. For example, the dual DC-DC converter20′ may be configured to supply power to two non-battery loads, such asmotors or resistive heaters. Additionally or alternatively, the dualDC-DC converter 20′ may be configured to supply power to one or morebatteries and also to one or more non-battery loads.

The dual DC-DC converter 20′ shown in FIG. 2 is similar in constructionto the example conventional DC-DC converter 20, as described above.However, instead of a single, common, output node 26, the dual DC-DCconverter 20′ includes a first output node 50 having a first DC outputvoltage V_(OUT1) and a second output node 52 having a second DC outputvoltage V_(OUT2), which may be different than the first DC outputvoltage V_(OUT1). A first smoothing capacitor 60 is connected betweenthe first output node 50 and the ground 42 to reduce ripple in the firstDC output voltage V_(OUT1). Similarly, a second smoothing capacitor 62is connected between the second output node 52 and the ground 42 toreduce ripple in the second DC output voltage V_(OUT2). A first battery22 is connected to the first output node 50 and a second battery 23 isconnected to the second output node 52. The switch sets 36, 38 may beoperated in an interleaved mode or a multiphase mode. Additional switchsets 36, 38 allow for smaller sized smoothing capacitors 60, 62 due tolower current ripple, but can also increase costs. Therefore, atrade-off in the number of switch sets 36, 38 must be made in designingthe DC-DC converter 20 for a given application.

A mode switch 70 is electrically connected between the output nodes 50,52 and may be opened to allow the dual DC-DC converter 20′ to beoperated with the each of the output nodes 50, 52 having differentvoltages. In this way, the batteries 22, 23 may be independentlycharged, particularly where they are unbalanced, for example, where thebatteries 22, 23 have different states of charge. The mode switch 70 maybe closed to provide electrical continuity between the output nodes 50,52 when the DC output voltages V_(OUT1), V_(OUT2) on each of thoseoutput nodes 50, 52 are equal to one another or are within apredetermined threshold.

With the mode switch 70 in a closed condition, the dual DC-DC converter20′ may operate similarly to a conventional DC-DC converter 20, but withthe two filter capacitors 46 connected together in parallel to provide alarger capacitance value than either of the two filter capacitors 46operating independently. This larger capacitance allows the dual DC-DCconverter 20′ to operate with lower ripple current. In other words, thedual DC-DC converter 20′ can provide its maximum charging power to bothof the batteries 22, 23 at the same time with the mode switch 70 in theclosed condition. The mode switch 70 may be controlled by the controller30 or by another processor or circuit, such as a voltage comparator. Insome embodiments, and as shown in FIG. 2, the controller 30 isconfigured to selectively assert a mode control line 72 to command themode switch 70 to be the closed condition or the opened condition.

The dual DC-DC converter 20′ may include three or more output nodes 50,52 and may include two or more mode switches 70 to provide selectiveisolation or connection therebetween. For example, a first mode switch70 may provide selective isolation between the first output node 50 andthe second output node 52, while a second mode switch (not shown) mayprovide selective isolation between the second output node 52 and athird output node (not shown). Furthermore, the dual DC-DC converter 20′may include any number of switch sets 36, 38, provided that there is atleast one switch set 36, 38 associated with each of the output nodes 50,52.

In some embodiments, where the dual DC-DC converter 20′ is configured asa battery charger, the first switch set 36 is configured to control thefirst DC output voltage V_(OUT1) the first output node 50 and to controla rate of charge into the first battery 22 connected thereto. The secondswitch set 38 is configured to control the second DC output voltageV_(OUT2) on to second output node 52 and to thereby control a rate ofcharge into the second battery 23 connected thereto. The mode switch 70is electrically connected between the output nodes 50, 52 and isoperable in a non-conductive mode to provide electrical isolationbetween the output nodes 50, 52 for allowing the batteries 22, 23 to becharged independently. The mode switch 70 is also operable in aconductive mode to provide electrical continuity between the outputnodes 50, 52. With the mode switch 70 in the conductive mode, thebatteries 22, 23 may be charged or discharged together.

In some embodiments where the dual DC-DC converter 20′ is configured asa battery charger, the controller 30 is configured to assert the modecontrol line 72 to cause the mode switch 70 to be in the conductive modein response to a difference between the first DC output voltage V_(OUT1)and the second DC output voltage V_(OUT2) being within a predeterminedthreshold. In other words, the first DC output voltage V_(OUT1) beingwithin the predetermined threshold of the second DC output voltageV_(OUT2), the batteries 22, 23 have a similar state of charge to oneanother, thus being able to be coupled together by the mode switch 70.

FIG. 3 is example schematic for another dual DC-DC converter 120 circuitin which four separate phase switches 128 each independently switch acommon DC electrical input V_(IN) having a high voltage (HV), such as400 to 600 VDC. The phase switches 128 may be operated in an interleavedmode or a multiphase mode. Each of the phase switches 128 may includeone or more of the switches 32, 34. The first two of the phase switches128, labeled “Phase 1” and “Phase 2” are each electrically connected toa first output node 50 which may operate at a low voltage (LV), such as3 to 48 VDC. A first filter capacitor 60 is connected between the firstoutput node 50 and a ground 42, and functions to reduce ripple in thefirst DC output voltage V_(OUT1) of the first output node 50 which canresult from the operation of the phase switches 128.

The second two of the phase switches 128, labeled “Phase 3” and “Phase4” are each electrically connected to a second output node 52, which mayalso operate at a low voltage (LV), such as 3 to 48 VDC. A second filtercapacitor 45 is connected between the second output node 52 and a ground42, and functions to reduce ripple in the second DC output voltageV_(OUT2) of the second output node 52 which can result from theoperation of the phase switches 128. One or more of the phase switches128 may also be configured to switch a ground 42 to one or more of theoutput nodes 50, 52.

A mode switch 70 is connected between the output nodes 50, 52, and maybe operated in an opened, or non-conducting condition, thus providingfor the output nodes 50, 52 to have DC output voltages V_(OUT1),V_(OUT2) with different values. The mode switch 70 may be closed toprovide electrical continuity between the output nodes 50, 52, thuscausing the DC output voltages V_(OUT1), V_(OUT2) to each have a samevalue. With the mode switch 70 in a closed condition, the output nodes50, 52 may be able to provide a higher current and with a moreconsistent DC voltage by using more of the phase switches 128 and with alarger, combined filter capacitor 60, 62 than when compared with theoutput nodes 50, 52 operating independently, with the mode switch 70 inthe opened condition.

Similarly to the dual DC-DC converter 20′ described above, the dualDC-DC converter 120 shown in FIG. 3 may include three or more outputnodes 50, 52 and may include two or more mode switches 70 to provideselective isolation or connection therebetween. Furthermore, the dualDC-DC converter 120 may include any number of phase switches 128,provided that there is at least one phase switch 128 associated witheach of the output nodes 50, 52.

A method 200 of operating a dual DC-DC converter 20′ is shown in theflow chart of FIG. 4. In some embodiments, the dual DC-DC converter 20′may be operated in accordance with the method 200 for charging two ormore batteries 22, 23.

The method 200 includes generating a first DC output voltage V_(OUT1)upon a first output node 50 by selectively switching a DC input voltageV_(IN) at step 202. In some embodiments, such as in the example dualDC-DC converter 20′ shown in FIG. 2, step 202 is performed using one ormore of the switches 32, 34 within the first switch set 36. Morespecifically, the controller 30 may command the one or more of theswitches 32, 34 within the first switch set 36 using a control scheme,such as a pulse width modulation (PWM) scheme to generate the first DCoutput voltage V_(OUT1) by controlling an amount of time that of one ormore of the switches 32, 34 within the first switch set 36 are energizedwithin a given time period. In some embodiments, such as in the exampledual DC-DC converter 20′ shown in FIG. 2, a first battery 22 isconnected between the first output node 50 and a ground 42.

The method 200 also includes generating a second DC output voltageV_(OUT2) upon a second output node 52 by selectively switching the DCinput voltage V_(IN) at step 204. In some embodiments, such as in theexample dual DC-DC converter 20′ shown in FIG. 2, step 204 is performedusing one or more of the switches 32, 34 within the second switch set38. More specifically, the controller 30 may command the one or more ofthe switches 32, 34 within the second switch set 38 using a controlscheme, such as a pulse width modulation (PWM) scheme to generate thesecond DC output voltage V_(OUT2) by controlling an amount of time thatof one or more of the switches 32, 34 within the second switch set 38are energized within a given time period. In some embodiments, such asin the example dual DC-DC converter 20′ shown in FIG. 2, a secondbattery 23 is connected between the second output node 52 and the ground42.

The method 200 also includes isolating the first output node 50 from thesecond output node 52 at step 206, thus providing for the second DCoutput voltage V_(OUT2) to be different than the first DC output voltageV_(OUT1). In some embodiments, such as in the example dual DC-DCconverter 20′ shown in FIG. 2, step 206 is performed by opening ormaintaining a mode switch 70 connected between output nodes 50, 52 in anopen or non-conducting condition.

In some embodiments, the method 200 also may include regulating acurrent provided to each of the output nodes 50, 52 at step 208. Forexample, each of the output nodes 50, 52 may be energized with a DCvoltage value that provides a current that does not exceed apredetermined current. In battery charging applications, thepredetermined current may be a predetermined maximum charging current tocharge the respective one of the batteries 22, 23 connected to each ofthe output nodes 50, 52. In some embodiments, the regulation of currentprovided to each of the output nodes 50, 52 may be performed only whenthe first output node 50 is isolated from the second output node 52. Insome embodiments, the example dual DC-DC converter 20′ may be configuredto monitor the electrical current being provided to each of thebatteries 22, 23 and to charge the batteries 22, 23 with a maximum safecharging current.

The method 200 continues with matching the DC output voltages V_(OUT1),V_(OUT2) at step 210. More specifically, step 210 includes changing atleast one of the DC output voltages V_(OUT1), V_(OUT2) on at least oneof the output nodes 50, 52 until the DC output voltages V_(OUT1),V_(OUT2) on the output nodes 50, 52 are equal or within a predeterminedthreshold, or voltage difference, from one another. In some embodiments,such as in the example dual DC-DC converter 20′ shown in FIG. 2, step210 is performed by changing the switching of one or more of theswitches 32, 34 within the first switch set 36 and/or the second switchset 38 by the controller 30. This step 208 may include balancing thecharge levels of the two batteries 22, 23 connected to the output nodes50, 52.

The method 200 continues with connecting the first output node 50 to thesecond output node 52 at step 212, thus providing for the second DCoutput voltage V_(OUT2) to be the same as the first DC output voltageV_(OUT1). In some embodiments, such as in the example dual DC-DCconverter 20′ shown in FIG. 2, step 212 is performed by closing ormaintaining a mode switch 70 connected between output nodes 50, 52 in aclosed or conducting condition. In some embodiments, the first outputnode 50 is connected to the second output node 52 at step 210 to provideelectrical continuity therebetween in response to the DC output voltagesV_(OUT1), V_(OUT2) on the output nodes 50, 52 being equal or within thepredetermined threshold from one another. In other words, step 212 maybe performed only after step 210 is complete. For example, the dualDC-DC converter 20′ may be configured to close the mode switch 70 if theDC output voltages V_(OUT1), V_(OUT2) on the output nodes 50, 52 areless than or equal to 0.5 volts of one-another. The mode switch 70 maybe controlled by the controller 30 or by another processor or circuit,such as a voltage comparator. In some embodiments, one or more timedelays or other prerequisites may also be required before the modeswitch 70 is allowed to be closed. Such other prerequisites may include,for example, the batteries 22, 23 being determined to be in workingorder, or the electrical current being supplied to one or both of thebatteries 22, 23 being within a predetermined value or range of values.

The system, methods and/or processes described above, and steps thereof,may be realized in hardware, software or any combination of hardware andsoftware suitable for a particular application. The hardware may includea general purpose computer and/or dedicated computing device or specificcomputing device or particular aspect or component of a specificcomputing device. The processes may be realized in one or moremicroprocessors, microcontrollers, embedded microcontrollers,programmable digital signal processors or other programmable device,along with internal and/or external memory. The processes may also, oralternatively, be embodied in an application specific integratedcircuit, a programmable gate array, programmable array logic, or anyother device or combination of devices that may be configured to processelectronic signals. It will further be appreciated that one or more ofthe processes may be realized as a computer executable code capable ofbeing executed on a machine readable medium.

The computer executable code may be created using a structuredprogramming language such as C, an object oriented programming languagesuch as C++, or any other high-level or low-level programming language(including assembly languages, hardware description languages, anddatabase programming languages and technologies) that may be stored,compiled or interpreted to run on one of the above devices as well asheterogeneous combinations of processors processor architectures, orcombinations of different hardware and software, or any other machinecapable of executing program instructions.

Thus, in one aspect, each method described above and combinationsthereof may be embodied in computer executable code that, when executingon one or more computing devices performs the steps thereof. In anotheraspect, the methods may be embodied in systems that perform the stepsthereof, and may be distributed across devices in a number of ways, orall of the functionality may be integrated into a dedicated, standalonedevice or other hardware. In another aspect, the means for performingthe steps associated with the processes described above may include anyof the hardware and/or software described above. All such permutationsand combinations are intended to fall within the scope of the presentdisclosure.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. A dual DC-DC converter comprising: a first switch set including afirst high-side switch and configured to generate a first DC outputvoltage upon a first output node by selectively closing the firsthigh-side switch to couple an input node having a DC input voltage to afirst common node; a second switch set including a second high-sideswitch and configured to generate a second DC output voltage upon asecond output node by selectively closing the second high-side switch tocouple the input node to a second common node; and a mode switchconfigured to selectively couple the first output node to the secondoutput node.
 2. The dual DC-DC converter of claim 1, wherein at leastone of the first switch set and the second switch set includes alow-side switch configured to selectively couple a ground to acorresponding one of the first common node or the second common node. 3.The dual DC-DC converter of claim 1, wherein each of the switch sets areoperated in an interleaved mode or multiphase mode.
 4. The dual DC-DCconverter of claim 1, further comprising a filter capacitor connectedbetween a ground and one of the output nodes.
 5. The dual DC-DCconverter of claim 1, further comprising an inductor connected betweenone of the common nodes and a corresponding one of the output nodes. 6.The dual DC-DC converter of claim 1, further comprising a controllerconfigured to control the DC output voltage on each of the output nodesby controlling switching of the first high-side switch within the firstswitch set and by controlling switching the second high-side switchwithin the second switch set by selectively asserting a control lineassociated with each of the high-side switches.
 7. The dual DC-DCconverter of claim 6, wherein the controller is configured to assert amode control line to selectively couple the first output node to thesecond output node.
 8. A battery charger comprising: a first switch setconfigured to control a first DC output voltage on a first output nodeand to control a rate of charge into a first battery connected thereto;a second switch set configured to control a second DC output voltage ona second output node and to control a rate of charge into a secondbattery connected thereto; a mode switch electrically connected betweenthe output nodes and operable in a non-conductive mode to provideelectrical isolation between the output nodes for allowing the firstbattery and the second battery to be charged independently; and whereinthe mode switch is operable in a conductive mode to provide electricalcontinuity between the output nodes.
 9. The battery charger of claim 8,further comprising: a controller configured to assert a mode controlline to cause the mode switch to be in the conductive mode; and whereinthe controller is configured to assert the mode control line in responseto a difference between the first DC output voltage and the second DCoutput voltage being within a predetermined threshold.
 10. A method ofoperating a dual DC-DC converter comprising: generating a first DCoutput voltage upon a first output node by switching a DC input voltage;generating a second DC output voltage upon a second output node byswitching the DC input voltage; and coupling the first output node tothe second output node with a mode control switch to cause the secondoutput voltage to be equal to the first output voltage.
 11. The methodof claim 10, further comprising regulating a current provided to each ofthe output nodes not to exceed a predetermined current.
 12. The methodof claim 10, further comprising changing at least one of the DC outputvoltages on at least one of the output nodes until the DC outputvoltages are within a predetermined voltage difference from one another.13. The method of claim 12, wherein changing at least one of the DCoutput voltages includes changing the switching of one or more switcheswithin a first switch set coupled to the first output node or changingthe switching of one or more switches within a second switch set coupledto the second output node.
 14. The method of claim 12, wherein changingat least one of the DC output voltages includes balancing a charge levelof a first battery connected to the first output node with a chargelevel of a second battery connected to the second output node.
 15. Themethod of claim 12, wherein the coupling the first output node to thesecond output node is performed in response to the DC output voltagesbeing within the predetermined voltage difference from one another. 16.The dual DC-DC converter of claim 1, further comprising an inductorconnected between the first common node and a corresponding one of theoutput nodes, and another inductor connected between the second commonnode and a corresponding one of the output nodes.
 17. The dual DC-DCconverter of claim 1, wherein the DC input voltage has a voltage of 400to 600 VDC.
 18. The battery charger of claim 8, wherein the first switchset includes a first high-side switch configured to selectively couplean input node having a DC input voltage to the first common node; andwherein the second switch set includes a second high-side switchconfigured to selectively couple the input node to the second commonnode.
 19. The battery charger of claim 8, wherein each of the switchsets are operated in an interleaved mode or multiphase mode.
 20. Thebattery charger of claim 8, wherein the DC input voltage has a voltageof 400 to 600 VDC.